Research On Optimization Of MAC In Wrieless Local Area Network

With the rapid development of wireless LAN, the density of the deployment of mobile network equipments is increasing enormously and people are also in need of more wireless services, such as the voice, the video and other real-time service. However, the limited radio resource makes the competition in channel more intensely. To improve the current situation, the researchers face many issues, which have become the important part of the backoff algorithm, including how to improve the transmission performance using the MAC protocol in order to reduce channel conflicts and ensure network fairness, and how to provide the timely, effective and stably services and offer different services to each different business.In this paper, we research on the optimization of the transmission performance in WLAN, which is based on improving network fairness, network throughput and providing different services. The main contributions of this paper are following:(1)Considering the inequities of BEB binary backoff algorithm, the paper proposes a fusion Backoff algorithm called FAEIED to improve the fairness of nodes accessing and reduce the non-essential backoff time. Based on EIED algorithm, the algorithm adds a threshold CWth to determine how fiercely the competition among the current channels and adjusts the contention window size according to the determination. Meanwhile, when the network load is light, the algorithm reduce the idle time of channels generated in each contention period through introducing the fast access mechanism of FCR algorithm so that improve the efficiency of node accessing, decrease the wasting back-off time of system and further improve the transmission performance.(2)The paper proposes a method of balancing the initial contention window of nodes in MAC protocol. The method distinguishs the setting of the initial contention window of node from each other according to their different priority levels, which results in a phenomenon that business with a high priority can have a higher probability of accessing channel. Through balancing the initial contention window size of nodes, the method identifies different services in light of different probabilities of accessing channel of businesses with different priority levels.(3)Concerned with the shortcoming of DCF mechanism that it cannot provide the function of distinguishing services based on priority levels, the paper puts forward a backoff algorithm called DSMAC which can identify different services. the algorithm realize the goal of differentiating services by adding a priority flag P to distinguish between different priority levels, modifying the initial contention window size in MAC layer of business, setting the number of retransmission based on the priority levels, and differentiate the backoff strategy of businesses with different priority levels.(4)Based on NS2 network simulation environment, the paper achieves the proposed MAC protocol and designs different simulation scenarios to compare with each other. The simulation results show that the FAEIED algorithm makes the fairness among nodes improved significantly and improves the throughput because of the introduction of the fast access mechanism. DSMAC algorithm enables nodes having higher-priority business to occupy more bandwidth as a result of reducing the average latency and packet loss probability.